A flying head type optical disk head wherein an optical head apparatus is divided to a fixed portion and a movable portion and the movable portion floats by a predetermined distance from an optical rotary recording medium, such as a magneto-optical disk, has been in practical use.
As a first related art of a flying head type magneto-optical head, FIG. 19 is a view which illustrates a “flying head type magneto-optical head” 22 wherein a wind pressure caused by rotation of a magneto-optical disk 210 is utilized to float a head portion in the focusing direction.
The magneto-optical head 220 comprises an optical block 221, a single actuator 222, a voice coil motor 223, a Galvano mirror 224 and an over light magnetic head 225 mounted on the single actuator 222, for performing data writing to a magneto-optical disk 210, such as an MD, rotated by a spindle motor 215 and data reading from the magneto-optical disk 210.
The optical block 221 comprises a laser diode, a beam spritter and a photo detector, etc. integrally as one body. Note that an object lens is provided at an end portion of the head near the over-light magnetic head 225 and separated from the optical block 221.
The voice coil motor 223 moves the single actuator 222 in one direction.
The voice coil motor 223 and the Galvano mirror 224 perform tracking control of the magneto-optical head 220.
A focus control is performed by the single actuator 222.
As a result that the over light magnetic head 225 floats from the surface of the magneto-optical disk 210 by leaving an exactly predetermined space due to a wind pressure caused by rotation of the magneto-optical disk 210, a focus distance is maintained.
A beam light emitted from a laser diode in the optical block 221 passes through the beam spritter, deflected by the Galvano mirror 224 and guided to the object lens positioned at the end of the head.
The object lens converges the beam light to make it expose a recording surface of the magneto-optical disk 210.
A reflection light from the magneto-optical disk 210 passes the object lens in the direction toward the Galvano mirror 224, and a return-back light deflected by the Galvano mirror 224 enters the beam spritter, deflected by the beam spritter and enters the photo detector. The photo detector is, for example, a four divided detector.
In the magneto-optical head 220, an optical system of the optical block 221 and the object lens are optically connected via the Galvano mirror 224.
As explained above, since only the object lens including the single actuator, a 45-degree mirror and the flying head are the movable portion, there is an advantage that the moving portion becomes compact.
However, the configuration of the magneto-optical head 220 for driving the single actuator 222 by the voice coil motor 223 is complicated and dimensions of the magneto-optical head 220 are large. Furthermore, since an optical path from the optical block 221 to the object lens is too long, optical reliability is low and it is hard to be more compact and lower in costs.
To attain a still larger capacity, a “multi-plate” optical recording/reproducing apparatus wherein a plurality of magneto-optical disks 210 having the complicated configuration as above are stacked along one rotation axis has been attempted, but it is virtually difficult to apply the above magneto-optical pickup to such an apparatus.
FIG. 20 is a view of the configuration of a magneto-optical head apparatus as a second related art of a flying head type magneto-optical head.
The magneto-optical head apparatus 320 is a flying head type magneto-optical head apparatus proposed by the TeraStor Corporation. The magneto-optical head apparatus performs data writing and data reading to and from a magneto-optical disk 310, such as an MD, rotated by a spindle motor (not shown). Therefore, the magneto-optical head apparatus 320 comprises a swing arm 321, a flying head type magneto-optical head 322 attached to one end portion of the arm 321, an object lens 327 mounted on the magneto-optical head 322, a magnetic modulation coil (not shown), a first mirror 323 provided at an upper portion of the magneto-optical head 322, a second mirror 324 provided on the arm 321, a voice coil motor 325 for performing tracking control by moving the arm 321 to rotate in the horizontal direction, and a light source module 326.
The light source module 326 comprises a laser diode, a beam splitter and a photo detector, etc. The photo detector is, for example, a four divided detector.
The object lens 327 is mounted on the magneto-optical head 322 and separated from the light source module 326.
The second mirror 324 and the first mirror 323 introduce a light beam from the laser diode in the light source module 326 to the object lens 327 mounted on the magneto-optical head 322. Namely, the beam light emitted from the laser diode in the light source module 326 passes the beam spritter and deflected to the first mirror 323 by the second mirror 324. The first mirror 323 deflects the incident light to the object lens 327. The object lens 327 converges the incident light to make it expose a recording surface of the magneto-optical disk 310.
The reflected light from the magneto-optical disk 310 passes through the object lens 327 mounted on the magneto-optical head 322, passes through the second mirror 324 from the first mirror 323, enters the beam spritter in the light source module 326 and reaches the photo detector.
The tracking control by the magneto-optical head 322 is preformed by swinging the arm 321 (a surface in parallel with the magneto-optical disk surface) in a range of a predetermined angle in the horizontal direction by driving the voice coil motor 325. The magneto-optical head 322 floats from the surface of the magneto-optical disk 310 by exactly a necessary distance for accessing due to a wind pressure caused by rotation of the magneto-optical disk 310. Accordingly, focus control is unnecessary.
Since the first mirror 323 or the second mirror 324 is driven by a micro actuator, there is an advantage that two-step tracking control, that is a coarse motion and a fine motion, becomes easy with the swing arm 321. However, the second prior art has problems listed below.
(1) In the magneto-optical head 320, since the arm 321 and the light source module 326 move integrally at the time of a near field recording operation, there are disadvantages that an inertia mass becomes large when moving the arm 321 and a seek time becomes long. Moreover, the voice coil motor 325 for outputting a considerably strong power is to be used. As a result, dimensions of the apparatus become large, it is hard to attain low cost, and there are limits for downsizing.
(2) In addition to the object lens 327 and the magnetic modulation coil, the first mirror 323 is mounted on the magneto-optical head 322 which floats in response to rotation of the magneto-optical disk 310, so that weight of the magneto-optical head 322 becomes large and a sufficient float value cannot be obtained in some cases.
(3) In the magneto-optical head 320, since a light path between the first mirror 323 and the second mirror 324 is open, there is a possibility that a disturbance light enters and reliability of a light propagation in the light path is not guaranteed. A method of using a polarized wave plane maintain type optical fiber instead of the first mirror 323 and the second mirror 324 is possible, but a decline of signal quality becomes a problem in that case.
Since the magneto-optical head 320 has large apparatus size, it is not suitable to a “multi-layered” multi plated magneto-optical recording/reproducing apparatus obtained by stacking a plurality of magneto-optical disks along one rotation axis.
FIG. 21 is a view of the configuration of a magneto-optical head apparatus as a third related art of a flying head type magneto-optical head.
The magneto-optical head apparatus 420 is a flying head type magneto-optical head apparatus proposed by the QUINTA Corporation.
The magneto-optical head apparatus 420 comprises an arm 421, gimbals 422 formed by an elastic member having flexibility fixed at an end of the arm 421, a slider 423 floating by a predetermined distance from a magneto-optical disk 410 fixed at an end of the gimbals 422, an object lens 424 mounted on the slider 423, an electro-static mirror 425, an optical system 426 provided between the electro-static mirror 425 and the object lens 424, an optical block 427 and an optical fiber 428 provided between the optical block 427 and the electro-static mirror 425.
The optical block 427 comprises a laser diode, a beam spritter and a photo detector, etc.
The photo detector is, for example, a four divided detector.
A beam light emitted from the laser diode in the optical block 427 passes through the beam spritter, enters the optical fiber 428, propagates in the optical fiber 428 to irradiate the electro-static mirror 425 to be deflected by the electro-static mirror 425, passes through the optical system 426, enters the object lens 424 to be converged by the object lens 424 and expose the recording surface of the magneto-optical disk 410.
A reflected light from the magneto-optical disk 410 passes an opposite light path from the above to enter the beam spritter in the optical block 427 to be deflected by the beam spritter and irradiate the photo detector.
In tracking control by the magneto-optical head 420, the arm 421 moves in a range of a predetermined angle on a surface in parallel with the magneto-optical disk surface (in the perpendicular direction with respect to the paper surface) by an actuator, such as a not shown voice coil motor, to be positioned at a predetermined track of the magneto-optical disk 410 by also using the electro-static mirror 425.
Since the slider 423 floats by a predetermined distance from the magneto-optical disk 410 due to a wind pressure caused by rotation of the magneto-optical disk 410, the object lens 424 is away from the magneto-optical disk 410 by exactly a predetermined distance. Accordingly, focus control is unnecessary.
However, the magneto-optical head 420 illustrated in FIG. 21 uses the optical fiber 428, so that there is a problem that the optical fiber 428 becomes a load on the rotating motion of the arm 421 to decline rotatable motion characteristics of the arm 421. Furthermore, since the optical fiber 428 and the electro-static mirror 425 perform optical coupling, there is a disadvantage that an optical coupling efficiency (coupling efficiency) becomes poor.
Moreover, in the magneto-optical head 420, a push-pull signal cannot be obtained, so that a sample servo has to be used for tracking control.
In an optical recording/reproducing apparatus, shortening of a wave length and increasing of a numerical aperture (NA) have been developed. For example, the NA was conventionally 0.5 or so, but recently, there are those having the NA of 0.9 in the far field range (FFR) and the NA of 1.4 or so in the near field range. A focus margin in such a state has to be, for example, ±0.158 in the FFR and ±10 nm to ±20 nm or so in the NFR, which is smaller than a conventional margin of ±1 μm. However, a focus margin as such can be secured in principle when applying the flying head type magneto-optical head configuration.
In actually, however, it is hard to attach an object lens to the flying head type magneto-optical head while securing accuracy of ±10 nm to ±20 nm or so in the NFR, and a problem of attachment accuracy arises. Furthermore, a position of attaching the object lens may shift due to temperature changes and humidity changes. Shift of a position as such is also hard to be prevented by adhesion.
As a method of overcoming problems as above, for example, as proposed in the Japanese Unexamined Patent Publication No. 7-65383, there is known a method of eliminating a DC focus amount by applying the configuration provided with an object lens attached with an electromagnetic actuator and adjusting the position mainly by the electromagnetic actuator. However, the flying head proposed by the Japanese Unexamined Patent Publication No. 7-65383 has a problem that dimensions of the flying head become large. When dimensions of the flying head become large, preferable flying (floating) characteristics cannot be attained and the price becomes high, as well.
As another method, for example, as proposed in the Japanese Unexamined Patent Publication No. 7-57284, there is known a method of eliminating a DC focus amount by providing a relay lens using two collimator lenses as illustrated in FIG. 22 to an optical fixed portion and adjusting a distance between the two lenses.
However, the flying head proposed in the Japanese Unexamined Patent Publication No. 7-57284 also has a problem that the dimensions become large because the distance is adjusted by using the two collimator lenses. Particularly, it is significant for the flying head type optical head apparatus used in near field recording to have very small dimensions. When the dimensions of the flying head become large, preferable flying (floating) characteristics cannot be attained. Furthermore, there is a problem that a price of the optical head apparatus becomes high.
There have been demands for a compact optical head and an optical recording/reproducing apparatus using the optical head which can be applied to a recent downsized magneto-optical recording medium and near field recording.
An increase of a recording capacity is furthermore demanded. As one method thereof, a “multilayered (multi plated)” magneto-optical recording/reproducing apparatus obtained by stacking a plurality of magneto-optical disks, etc. along one rotation axis has been desired, and a magneto-optical head, a magneto-optical pickup and other optical heads suitable to such a multi plated magneto-optical recording/reproducing apparatus have been demanded.
The flying head proposed in the Japanese Unexamined Patent Publication No. 7-57284, however, hardly realizes a so called “multilayered (or multi-plated)” optical recording/reproducing apparatus attempting downsizing and increasing of a memory capacity by stacking a plurality of magneto-optical disks along a rotation axis of a motor for rotating a magneto-optical disk.
In the flying head, it is known that a float value of a slider fluctuates, and it is preferable to correct the fluctuation of the float value as such to attain more accurate focus control. Since such fluctuation of the float amount has a high frequency, it is considered to be AC components.
A magneto-optical head or a magneto-optical pickup used in a magneto-optical disk has been explained as prior arts above, but an optical pickup, etc. for performing signal reading only by an optical signal also encounter similar problems as above.